Method and apparatus for supporting local gateway service for dual connectivity in wireless communication system

ABSTRACT

A method and apparatus for supporting a local gateway (L-GW) service in a wireless communication system is provided. When an L-GW is co-located with a master evolved NodeB (MeNB) in dual connectivity, a secondary evolved NodeB (SeNB) in dual connectivity receives a request message including information on a specific E-UTRAN radio access bearer (E-RAB), which is served by a L-GW, from a master evolved NodeB (MeNB) in dual connectivity which has the L-GW, decides to transmit data via a X2 interface instead of a S1-U interface for the specific E-RAB, and transmits a response message to the MeNB.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2015/011655, filed on Nov. 2, 2015,which claims the benefit of U.S. Provisional Application No. 62/078,951,filed on Nov. 12, 2014, the contents of which are all herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for supporting local gateway(L-GW) service for dual connectivity in a wireless communication system.

Related Art

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

Small cells using low power nodes are considered promising to cope withmobile traffic explosion, especially for hotspot deployments in indoorand outdoor scenarios. A low-power node generally means a node whosetransmission power is lower than macro node and base station (BS)classes, for example pico and femto evolved NodeB (eNB) are bothapplicable. Small cell enhancements for evolved UMTS terrestrial radioaccess (E-UTRA) and evolved UMTS terrestrial radio access network(E-UTRAN) will focus on additional functionalities for enhancedperformance in hotspot areas for indoor and outdoor using low powernodes.

One of potential solutions for small cell enhancement, dual connectivityhas been discussed. Dual connectivity is used to refer to operationwhere a given user equipment (UE) consumes radio resources provided byat least two different network points connected with non-ideal backhaul.Furthermore, each eNB involved in dual connectivity for a UE may assumedifferent roles. Those roles do not necessarily depend on the eNB'spower class and can vary among UEs. Dual connectivity may be one ofpotential solutions for small cell enhancement.

The LTE network architecture is designed for the centralized gatewayswhere the operator typically only has one or a few gateways. Thatarchitecture makes sense for the Internet access because the number ofInternet peering points is limited. Different architecture, however, maybe needed for the small base stations to allow access to the localcontent. The local access would be practical for accessing corporateintranet information or accessing a home network over LTE radio.

A method for supporting a local gateway (L-GW) service for dualconnectivity may be required.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for supportinglocal gateway (L-GW) service for dual connectivity in a wirelesscommunication system. The present invention provides a method andapparatus for indicating that an L-GW is used for a specific E-UTRANradio access bearer (E-RAB), when an L-GW is co-located with a masterevolved NodeB (MeNB) in dual connectivity.

In an aspect, a method for supporting, by a secondary evolved NodeB(SeNB) in dual connectivity, a local gateway (L-GW) service in awireless communication system is provided. The method includes receivinga request message including information on a specific E-UTRAN radioaccess bearer (E-RAB), which is served by a L-GW, from a master evolvedNodeB (MeNB) in dual connectivity which has the L-GW, deciding totransmit data via a X2 interface instead of a S1-U interface for thespecific E-RAB, and transmitting a response message to the MeNB.

In another aspect, a secondary evolved NodeB (SeNB) in dual connectivityis provided. The SeNB includes a memory, a transceiver, and a processorcoupled to the memory and the transceiver, and configured to control thetransceiver to receive a request message including information on aspecific E-UTRAN radio access bearer (E-RAB), which is served by a localgateway (L-GW), from a master evolved NodeB (MeNB) in dual connectivitywhich has the L-GW, decide to transmit data via a X2 interface insteadof a S1-U interface for the specific E-RAB, and control the transceiverto transmit a response message to the MeNB.

An L-GW can be supported efficiently in dual connectivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem.

FIG. 4 shows a block diagram of a control plane protocol stack of an LTEsystem.

FIG. 5 shows an example of a physical channel structure.

FIG. 6 shows radio protocol architecture for dual connectivity.

FIG. 7 shows C-plane connectivity of eNBs involved in dual connectivityfor a certain UE.

FIG. 8 shows U-plane connectivity of eNBs involved in dual connectivityfor a certain UE.

FIG. 9 shows an example of U-plane architecture for dual connectivity.

FIG. 10 shows another example of U-plane architecture for dualconnectivity.

FIG. 11 shows an example of architecture of dual connectivity in whichan L-GW locates together with a MeNB.

FIG. 12 show a method for supporting L-GW service for dual connectivityaccording to an embodiment of the present invention.

FIG. 13 show a method for supporting L-GW service for dual connectivityaccording to another embodiment of the present invention.

FIG. 14 shows a wireless communication system to implement an embodimentof the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), anaccess point, etc. One eNB 20 may be deployed per cell.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) and a systemarchitecture evolution (SAE) gateway (S-GW). The MME/S-GW 30 may bepositioned at the end of the network and connected to an externalnetwork. For clarity, MME/S-GW 30 will be referred to herein simply as a“gateway,” but it is understood that this entity includes both the MMEand S-GW.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), packet data network (PDN)gateway (P-GW) and S-GW selection, MME selection for handovers with MMEchange, serving GPRS support node (SGSN) selection for handovers to 2Gor 3G 3GPP access networks, roaming, authentication, bearer managementfunctions including dedicated bearer establishment, support for publicwarning system (PWS) (which includes earthquake and tsunami warningsystem (ETWS) and commercial mobile alert system (CMAS)) messagetransmission. The S-GW host provides assorted functions includingper-user based packet filtering (by e.g., deep packet inspection),lawful interception, UE Internet protocol (IP) address allocation,transport level packet marking in the DL, UL and DL service levelcharging, gating and rate enforcement, DL rate enforcement based onaccess point name aggregate maximum bit rate (APN-AMBR).

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 is connected to the eNB 20 via a Uu interface. The eNBs 20 areconnected to each other via an X2 interface. Neighboring eNBs may have ameshed network structure that has the X2 interface. A plurality of nodesmay be connected between the eNB 20 and the gateway 30 via an S1interface.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC. Referring to FIG. 2, the eNB 20 may perform functions ofselection for gateway 30, routing toward the gateway 30 during a radioresource control (RRC) activation, scheduling and transmitting of pagingmessages, scheduling and transmitting of broadcast channel (BCH)information, dynamic allocation of resources to the UEs 10 in both ULand DL, configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE_IDLE state management,ciphering of the user plane, SAE bearer control, and ciphering andintegrity protection of NAS signaling.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem. FIG. 4 shows a block diagram of a control plane protocol stackof an LTE system. Layers of a radio interface protocol between the UEand the E-UTRAN may be classified into a first layer (L1), a secondlayer (L2), and a third layer (L3) based on the lower three layers ofthe open system interconnection (OSI) model that is well-known in thecommunication system.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Databetween the MAC layer and the PHY layer is transferred through thetransport channel. Between different PHY layers, i.e., between a PHYlayer of a transmission side and a PHY layer of a reception side, datais transferred via the physical channel.

MAC layer, a radio link control (RLC) layer, and a packet dataconvergence protocol (PDCP) layer belong to the L2. The MAC layerprovides services to the RLC layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides data transferservices on logical channels. The RLC layer supports the transmission ofdata with reliability. Meanwhile, a function of the RLC layer may beimplemented with a functional block inside the MAC layer. In this case,the RLC layer may not exist. The PDCP layer provides a function ofheader compression function that reduces unnecessary control informationsuch that data being transmitted by employing IP packets, such as IPv4or IPv6, can be efficiently transmitted over a radio interface that hasa relatively small bandwidth.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer controls logical channels, transportchannels, and physical channels in relation to the configuration,reconfiguration, and release of radio bearers (RBs). The RB signifies aservice provided the L2 for data transmission between the UE andE-UTRAN.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid ARQ (HARQ). The PDCP layer (terminatedin the eNB on the network side) may perform the user plane functionssuch as header compression, integrity protection, and ciphering.

Referring to FIG. 4, the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The RRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

FIG. 5 shows an example of a physical channel structure. A physicalchannel transfers signaling and data between PHY layer of the UE and eNBwith a radio resource. A physical channel consists of a plurality ofsubframes in time domain and a plurality of subcarriers in frequencydomain. One subframe, which is 1 ms, consists of a plurality of symbolsin the time domain. Specific symbol(s) of the subframe, such as thefirst symbol of the subframe, may be used for a physical downlinkcontrol channel (PDCCH). The PDCCH carries dynamic allocated resources,such as a physical resource block (PRB) and modulation and coding scheme(MCS).

A DL transport channel includes a broadcast channel (BCH) used fortransmitting system information, a paging channel (PCH) used for paginga UE, a downlink shared channel (DL-SCH) used for transmitting usertraffic or control signals, a multicast channel (MCH) used for multicastor broadcast service transmission. The DL-SCH supports HARQ, dynamiclink adaptation by varying the modulation, coding and transmit power,and both dynamic and semi-static resource allocation. The DL-SCH alsomay enable broadcast in the entire cell and the use of beamforming.

A UL transport channel includes a random access channel (RACH) normallyused for initial access to a cell, a uplink shared channel (UL-SCH) fortransmitting user traffic or control signals, etc. The UL-SCH supportsHARQ and dynamic link adaptation by varying the transmit power andpotentially modulation and coding. The UL-SCH also may enable the use ofbeamforming.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting multimedia broadcast multicast services(MBMS) control information from the network to a UE. The DCCH is apoint-to-point bi-directional channel used by UEs having an RRCconnection that transmits dedicated control information between a UE andthe network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC idle state (RRC_IDLE) and anRRC connected state (RRC_CONNECTED). In RRC_IDLE, the UE may receivebroadcasts of system information and paging information while the UEspecifies a discontinuous reception (DRX) configured by NAS, and the UEhas been allocated an identification (ID) which uniquely identifies theUE in a tracking area and may perform public land mobile network (PLMN)selection and cell re-selection. Also, in RRC_IDLE, no RRC context isstored in the eNB.

In RRC_CONNECTED, the UE has an E-UTRAN RRC connection and a context inthe E-UTRAN, such that transmitting and/or receiving data to/from theeNB becomes possible. Also, the UE can report channel qualityinformation and feedback information to the eNB. In RRC_CONNECTED, theE-UTRAN knows the cell to which the UE belongs. Therefore, the networkcan transmit and/or receive data to/from UE, the network can controlmobility (handover and inter-radio access technologies (RAT) cell changeorder to GSM EDGE radio access network (GERAN) with network assistedcell change (NACC)) of the UE, and the network can perform cellmeasurements for a neighboring cell.

In RRC_IDLE, the UE specifies the paging DRX cycle. Specifically, the UEmonitors a paging signal at a specific paging occasion of every UEspecific paging DRX cycle. The paging occasion is a time interval duringwhich a paging signal is transmitted. The UE has its own pagingoccasion. A paging message is transmitted over all cells belonging tothe same tracking area. If the UE moves from one tracking area (TA) toanother TA, the UE will send a tracking area update (TAU) message to thenetwork to update its location.

Overall architecture and network interface for dual connectivity (DC) isdescribed. It may be referred to 3GPP TR 36.842 V12.0.0 (2013-12). TheE-UTRAN supports dual connectivity operation whereby a multiple RX/TX UEin RRC_CONNECTED is configured to utilize radio resources provided bytwo distinct schedulers, located in two eNBs connected via a non-idealbackhaul over the X2 interface. The overall E-UTRAN architecturedescribed in FIG. 1 is applicable for dual connectivity as well. Twodifferent roles may be assumed to eNBs involved in dual connectivity fora certain UE: an eNB may either act as a master eNB (MeNB) or as asecondary eNB (SeNB). The MeNB is the eNB which terminates at leastS1-MME in dual connectivity. The SeNB is the eNB that is providingadditional radio resources for the UE but is not the MeNB in dualconnectivity. In dual connectivity a UE is connected to one MeNB and oneSeNB.

FIG. 6 shows radio protocol architecture for dual connectivity. In DC,the radio protocol architecture that a particular bearer uses depends onhow the bearer is setup. Three alternatives exist, master cell group(MCG) bearer, secondary cell group (SCG) bearer and split bearer.Referring to FIG. 6, those three alternatives are depicted, i.e. inorder of the MCG bearer, split bearer and SCG bearer from left to right.The MCG bearer is a bearer whose radio protocols are only located in theMeNB to use MeNB resources only in dual connectivity. The SCG bearer isa bearer whose radio protocols are only located in the SeNB to use SeNBresources in dual connectivity. The split bearer is a bearer whose radioprotocols are located in both the MeNB and the SeNB to use both MeNB andSeNB resources in dual connectivity. Signaling radio bearers (SRBs) arealways of the MCG bearer and therefore only use the radio resourcesprovided by the MeNB. The MCG is a group of serving cells associatedwith the MeNB, comprising of the primary cell (PCell) and optionally oneor more secondary cells (SCells) in dual connectivity. The SCG is agroup of serving cells associated with the SeNB, comprising of primarySCell (PSCell) and optionally one or more SCells in dual connectivity.DC may also be described as having at least one bearer configured to useradio resources provided by the SeNB.

FIG. 7 shows C-plane connectivity of eNBs involved in dual connectivityfor a certain UE. Inter-eNB control plane signaling for dualconnectivity is performed by means of X2 interface signaling. Controlplane signaling towards the MME is performed by means of S1 interfacesignaling. There is only one S1-MME connection per UE between the MeNBand the MME. Each eNB should be able to handle UEs independently, i.e.provide the PCell to some UEs while providing SCell(s) for SCG toothers. Each eNB involved in dual connectivity for a certain UE owns itsradio resources and is primarily responsible for allocating radioresources of its cells, respective coordination between MeNB and SeNB isperformed by means of X2 interface signaling. Referring to FIG. 7, theMeNB is C-plane connected to the MME via S1-MME, the MeNB and the SeNBare interconnected via X2-C.

FIG. 8 shows U-plane connectivity of eNBs involved in dual connectivityfor a certain UE. U-plane connectivity depends on the bearer optionconfigured. For MCG bearers, the MeNB is U-plane connected to the S-GWvia S1-U, the SeNB is not involved in the transport of user plane data.For split bearers, the MeNB is U-plane connected to the S-GW via S1-Uand in addition, the MeNB and the SeNB are interconnected via X2-U. ForSCG bearers, the SeNB is directly connected with the S-GW via S1-U. Ifonly MCG and split bearers are configured, there is no S1-U terminationin the SeNB.

FIG. 9 shows an example of U-plane architecture for dual connectivity.U-plane architecture for dual connectivity shown in FIG. 9 is thecombination of S1-U that terminates in SeNB and independent PDCPs (nobearer split). U-plane architecture for dual connectivity shown in FIG.9 may be called “Architecture 1A”.

FIG. 10 shows another example of U-plane architecture for dualconnectivity. U-plane architecture for dual connectivity shown in FIG.10 is the combination of S1-U that terminates in MeNB, bearer split inMeNB, and independent RLCs for split bearers. U-plane architecture fordual connectivity shown in FIG. 10 may be called “Architecture 3C”.

Local IP access (LIPA) function enables a UE to access directlyenterprise or residential network without user plane data travellingfirst to the centralized gateway. LIPA functionality would make sensetogether with home eNB (HeNB). A local gateway (L-GW) is co-located witha femto for the local access. The L-GW supports of internal direct userplane path with the HeNB.

Dual connectivity was introduced in 3GPP LTE rel-12. Further,LIPA/selected IP traffic offload (SIPTO) was introduced in the pastreleases. A potential architecture of 3GPP LTE rel-13 is that the L-GWis supported for dual connectivity.

FIG. 11 shows an example of architecture of dual connectivity in whichan L-GW locates together with a MeNB. Referring to FIG. 11, servicelocal breakout may be performed at the L-GW. Since the L-GW co-locateswith the MeNB, X2-U interface between the MeNB and SeNB may be used totransfer user data instead of S1-U interface between the SeNB and S-GW.However in this case, how the E-UTRAN radio access bearer (E-RAB) can beserved by the L-GW has not yet defined clearly.

In order to solve the problem described above, a method for supportingL-GW service for dual connectivity when the L-GW is co-located with theMeNB, may be proposed according to an embodiment of the presentinvention.

FIG. 12 show a method for supporting L-GW service for dual connectivityaccording to an embodiment of the present invention.

In step S100, the MeNB decides to request the SeNB to allocate radioresources for a specific E-RAB, and accordingly, transmits the SeNBAddition Request message to the SeNB. The SeNB Addition Request messagemay indicate characteristics of the specific E-RAB, which may includeE-RAB parameters, transport network layer (TNL) address informationcorresponding to the UP option. If the corresponding specific E-RAB isserved by the L-GW, the SeNB Addition Request message may include atleast one of an indication that L-GW is to be used for the correspondingspecific E-RAB, correlation identifier (ID), or the MeNB GPRS tunnelingprotocol (GTP) tunnel endpoint ID (TEID). The MeNB GTP TEID may be usedfor the corresponding specific E-RAB in order to use X2 interface fordata transmission, especially for SCG bearer option.

Upon receiving the SeNB Addition Request message, in step S110, the SeNBmakes a decision to transmit data through X2 interface instead of S1-Uinterface for the specific E-RAB.

Upon deciding to transmit data through X2 interface for the specificE-RAB, in step S120, the SeNB gives a response to the MeNB for the SeNBAddition Request message by transmitting the SeNB Addition RequestAcknowledge message to the MeNB. If the corresponding specific E-RAB isserved by the L-GW, the SeNB Addition Request Acknowledge message mayinclude at least one of X2 DL GTP tunnel endpoint/or SeNB GTP tunnelendpoint, or an indication for the admitted E-RABs to be served by theL-GW.

In step S130, the MeNB transmit the RRCConnectionReconfiguration messageto the UE. In step S140, the UE transmit theRRCConnectionReconfigurationComplete message to the MeNB. In step S150,the MeNB transmit the SeNB Reconfiguration Complete message to the SeNB.In step S160, the UE and the SeNB performs the random access procedure.In step S170, the MeNB may transmit the SN Status Transfer message tothe SeNB. In step S180, data forwarding may be performed.

FIG. 13 show a method for supporting L-GW service for dual connectivityaccording to another embodiment of the present invention.

In step S200, the SeNB in dual connectivity receives a request messageincluding information on a specific E-RAB, which is served by an L-GW,from a MeNB in dual connectivity which has the L-GW. The request messagemay request the SeNB to allocate radio resource for the specific E-RAB.The request message may further include at least one of an indicationthat the L-GW is to be used for the specific E-RAB, a correlation ID, ora MeNB GTP TEID. The correlation ID may include a SIPTO correlation IDor a LIPA correlation ID. The request message may be a SeNB AdditionRequest message or a SeNB Modification Request message. The informationon the specific E-RAB may include at least one of E-RAB parameters forthe specific E-RAB, or TNL address information for the specific E-RAB.

In step S210, the SeNB decides to transmit data via an X2 interfaceinstead of a S1-U interface for the specific E-RAB.

In step S210, the SeNB transmits a response message to the MeNB. Theresponse message may include at least one of a X2 DL GTP tunnelendpoint, a SeNB GTP tunnel endpoint, or an indication for the specificE-RAB to be served by the L-GW. The response message may be a SeNBAddition Request Acknowledge message or a SeNB Modification RequestAcknowledge message.

FIG. 14 shows a wireless communication system to implement an embodimentof the present invention.

A MeNB 800 may include a processor 810, a memory 820 and a transceiver830. The processor 810 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 810. The memory 820 is operatively coupled with the processor810 and stores a variety of information to operate the processor 810.The transceiver 830 is operatively coupled with the processor 810, andtransmits and/or receives a radio signal.

A SeNB 900 may include a processor 910, a memory 920 and a transceiver930. The processor 910 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 910. The memory 920 is operatively coupled with the processor910 and stores a variety of information to operate the processor 910.The transceiver 930 is operatively coupled with the processor 910, andtransmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The transceivers 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What is claimed is:
 1. A method for a secondary evolved NodeB (SeNB) indual connectivity in a wireless communication system, the methodcomprising: receiving a request message including information on aspecific evolved universal mobile telecommunication system (UMTS)terrestrial radio access network (E-UTRAN) radio access bearer (E-RAB),which is served by a local gateway (L-GW), from a master evolved NodeB(MeNB) in dual connectivity which is collocated with the L-GW; decidingto transmit data via a X2 interface instead of a S1-U interface for thespecific E-RAB; and transmitting a response message to the MeNB.
 2. Themethod of claim 1, wherein the request message requests the SeNB toallocate radio resource for the specific E-RAB.
 3. The method of claim1, wherein the request message further includes at least one of anindication that the L-GW is to be used for the specific E-RAB, acorrelation identifier (ID), or a MeNB general packet radio service(GPRS) tunneling protocol (GTP) tunnel endpoint ID (TEID).
 4. The methodof claim 3, wherein the correlation ID includes a selected Internetprotocol (IP) traffic offload (SIPTO) correlation ID or a local IP(LIPA) correlation ID.
 5. The method of claim 1, wherein the requestmessage is a SeNB Addition Request message or a SeNB ModificationRequest message.
 6. The method of claim 1, wherein the information onthe specific E-RAB includes at least one of E-RAB parameters for thespecific E-RAB, or transport network layer (TNL) address information forthe specific E-RAB.
 7. The method of claim 1, wherein the responsemessage includes at least one of a X2 downlink (DL) general packet radioservice (GPRS) tunneling protocol (GTP) tunnel endpoint, a SeNB GTPtunnel endpoint, or an indication for the specific E-RAB to be served bythe L-GW.
 8. The method of claim 1, wherein the response message is aSeNB Addition Request Acknowledge message or a SeNB Modification RequestAcknowledge message.
 9. A secondary evolved NodeB (SeNB) in dualconnectivity comprising: a memory; a transceiver; and a processorcoupled to the memory and the transceiver, and configured to: controlthe transceiver to receive a request message including information on aspecific evolved universal mobile telecommunication system (UMTS)terrestrial radio access network (E-UTRAN) radio access bearer (E-RAB),which is served by a local gateway (L-GW), from a master evolved NodeB(MeNB) in dual connectivity which is collocated with the L-GW; decide totransmit data via a X2 interface instead of a S1-U interface for thespecific E-RAB; and control the transceiver to transmit a responsemessage to the MeNB.
 10. The SeNB of claim 9, wherein the requestmessage requests the SeNB to allocate radio resource for the specificE-RAB.
 11. The SeNB of claim 9, wherein the request message furtherincludes at least one of an indication that the L-GW is to be used forthe specific E-RAB, a correlation identifier (ID), or a MeNB generalpacket radio service (GPRS) tunneling protocol (GTP) tunnel endpoint ID(TEID).
 12. The SeNB of claim 9, wherein the request message is a SeNBAddition Request message or a SeNB Modification Request message.
 13. TheSeNB of claim 9, wherein the information on the specific E-RAB includesat least one of E-RAB parameters for the specific E-RAB, or transportnetwork layer (TNL) address information for the specific E-RAB.
 14. TheSeNB of claim 9, wherein the response message includes at least one of aX2 downlink (DL) general packet radio service (GPRS) tunneling protocol(GTP) tunnel endpoint, a SeNB GTP tunnel endpoint, or an indication forthe specific E-RAB to be served by the L-GW.
 15. The SeNB of claim 9,wherein the response message is a SeNB Addition Request Acknowledgemessage or a SeNB Modification Request Acknowledge message.